It wasn't especially long ago that Australia's mining and energy giant, BHP Billiton (NYSE: BHP), was one of the stars of the proverbial midway. Today, however, along with a bevy of other industrial powerhouses, including giant equipment manufacturer Caterpillar (NYSE: CAT) -- which is temporarily shutting down parts of its Decatur, Ill., truck plant -- BHP is hunkering down in the face of a worldwide economic slowdown, especially as it relates to China.

But having watched the Melbourne-based company for a number of years, I remain convinced that BHP Billiton continues to merit close attention from Foolish investors. After all, while the economic softening in the world's second-largest economy has had a profound effect on a host of commodities, especially iron ore, BHP continues to expand its energy practice, something that's essentially foreign to the other big minerals miners. At some point, likely in the not-too-distant future, the company will benefit from a combined strengthening in both of its businesses.

A host of important products
As a quick refresher, BHP is involved in an array of mining operations, producing base metals such as lead, silver, zinc, copper, gold, and molybdenum. Beyond that, its output includes primary aluminum, manganese alloy, iron ore, metallurgical coal, energy coal, and last -- but hardly least -- petroleum.

As you likely know, China's pullback in steel manufacturing has resulted in a decline in the demand for iron ore, a phenomenon that has hit BHP and its Anglo-Australian peer Rio Tinto (NYSE: RIO), among others. The effects have also fallen heavily on the Australian economy, which has been a relative powerhouse thanks to its treasure trove of natural resources. One consequence, to the surprise of most economists, was the Reserve Bank of Australia cutting its benchmark lending rate by 0.25% to 3.25%.

As you might expect, the country's -- indeed, the world's -- expanding economic woes have resulted in a reduction in capital spending plans by BHP Billiton and the other big miners in Australia. In BHP's case, management has vowed not to approve any big new projects until at least mid-2013. Effectively sent to the sideline are a proposed potash mine in Canada, an expansion of the Port Hedland iron ore facility, and its ambitious Olympic Dam project. Australia's Olympic Dam contains the world's largest uranium reserves, along with a big copper find and recoverable gold and silver.

Part and parcel of the cost reductions will be new assignments and layoffs of employees in iron ore, the company's biggest operation. The mineral, for which BHP is the world's third-largest supplier, resulted in revenue approaching $23 billion during its June fiscal year.

Compelling and continuing energy expansion
But despite these clouds, my lingering interest with the company is largely related to the continued expansion of its petroleum operations. Quite simply, despite soft North American natural-gas prices, I don't see crude prices declining appreciably, especially with the Middle East having achieved tinderbox status. And so, if the World Bank is anywhere close to accurate in its prediction that China's growth will come in at about 7.7% this year -- down from 9.3% last year and 10.4% in 2010 -- there likely will come a day within the investing time horizons of most Fools when both minerals and petroleum will ring the cash register loudly for the company.

In petroleum, the company is spread virtually worldwide, with U.S. projects on land and in the Gulf of Mexico, along with activities in Australia, the United Kingdom, Africa, the Middle East, and Asia. Not all of these operations have been raging successes, however. Early last year, BHP paid $4.75 billion for Chesapeake Energy's (NYSE: CHK) Fayetteville Shale assets, and, based on dwindling natural-gas prices, wrote down that purchase by a sobering $2.84 billion in August. I nevertheless tend toward being sanguine about the growth of natural-gas usage in the U.S., so I won't fault the longer-term wisdom of the acquisition.

More purchases in the offing?
Later in the year, the company spent $12.1 billion to acquire Petrohawk Energy, which gave it an entry into the Haynesville Shale, the Permian Basin, and Texas's hot Eagle Ford play, where Petrohawk was the first company to drill a successful well. Now, despite being a significant holder of Gulf of Mexico assets, it appears that BHP is considering acquiring a portion of Petrobras' (NYSE: PBR) properties there. The state-controlled Brazilian company owns more than 100 blocks in the U.S. Gulf and is seeking to raise funds to cover operating costs off its own shores.

Beyond these operating considerations, there are a few metrics that, to my mind, make BHP attractive, even as it girds for more challenging times. For instance, as my Foolish colleague Sean Williams pointed out just last week, the company's dividend has grown at a rate of 23.6% over the past decade, and at an indicated forward rate of 3.3%, it appears sustainable. Beyond that, its 36.8% operating margin is impressive, and given the capital-intensive nature of its businesses, its 14.4% return on assets isn't chicken feed, especially when compared to the company's peers.

The Foolish bottom line
I'm not suggesting that you drop everything and back up the truck to acquire BHP Billiton shares. However, I'd hardly argue against slowly building -- or adding to -- a position in the big company. Otherwise, it seems you'd be wise to add its name to My Watchlist.

Beyond that, I mentioned Caterpillar above. Caterpillar is the market share leader in an industry in which size matters, and its quality products, extensive service network, and unparalleled brand strength combine to give it solid competitive advantages. Read all about Caterpillar's strengths and weaknesses in our brand-new report. Just click here to access it now.